A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In device manufacturing methods using lithographic projection apparatus, an important factor is accuracy. A pattern of a patterning device being projected onto a target portion of a substrate will generally not result in a miniaturized desired version of the pattern on the substrate. Causes include a non-uniform source-power spectrum, resist sensitivity characteristics and stray radiation, the latter also referred to as flare. These sources of perturbation may result in an overexposure, i.e. a dose which is too high, for a certain type of structure e.g. a dense pattern and an underexposure, i.e. a dose which is too low, for a different type of structure, e.g. an isolated feature. Many systematic perturbation factors may have an impact on the long range dose, i.e. they have an influence on the substrate over distances on the substrate to be exposed exceeding 1 mm. Examples of systematic perturbation factors include stray radiation and out-of-band radiation, i.e. radiation with a wavelength outside the actinic sensitivity range of resist provided on a substrate that is to be exposed.